One or more of degradation, drift, or non-reproducibility of hardware of a spectroscopic analysis system can affect frequency and wavelength registration and therefore the accuracy and reproducibility of measurements made using such a system. These effects are generally inevitable in real-world applications of spectroscopic analysis. Hardware of a spectroscopic analysis system can include light sources (e.g. lamps, lasers, or the like), electronics, optics, mechanical components, and the like. Achieving and maintaining accurate and reproducible frequency and wavelength registration of absorbance spectral data can be an important consideration in quantitative spectroscopy.
Currently available approaches to addressing these issues have included reference cell technologies that use in-line or split beam path configurations, periodic checks of frequency and/or wavelength registration using validation gas or gas mixtures, and peak tracking of one or more strong spectral peaks of a target analyte and/or another “background” compound present in a sample fluid to correct for frequency registration deviations. However, reference or validation cells (e.g., as described in co-owned U.S. Pat. No. 8,358,417, which is incorporated herein by reference) can require additional hardware installation and potentially add complexity to analytical system design. Periodic frequency or wavelength registration checks using one or more standard gases or gas mixtures generally require switching mechanisms for a fluid (e.g. gas or liquid) containing a known concentration of the target analyte or another compound (which may or may not be present in the process sample fluid) that absorbs light in the target wavelength region, in addition to a supply of the consumable standardized fluid. This approach also interrupts continuous process measurements, which can lead to significant measurement blind time while performing system validations. Peak tracking approaches can be susceptible to background fluid composition changes as well as temperature and pressure effects. Additionally, while peak tracking generally can be used to correct linear frequency registration deviation, it typically provides fewer benefits in correcting for non-linear frequency registration deviation.